1. Field of the Invention
The present invention relates to methods for manufacturing a magnetic sensor having electrode layers provided on an upper and a lower side of a multilayer film exhibiting a magnetoresistance effect, and more particularly, relates to a method for manufacturing a magnetic sensor which can easily and accurately form a current path-squeezing structure in which a current path flowing through the multilayer film is squeezed.
2. Description of the Related Art
In a current perpendicular to the plane (CPP) type magnetic sensor in which individual layers, that is, a free magnetic layer, non-magnetic conductive layer, a fixed magnetic layer, and an antiferromagnetic layer are laminated to each other in the thickness direction, and in which current flows in the direction perpendicular to the film surface of this multilayer film, it has been understood that unless the total film thickness of the multilayer film is increased, and an area (hereinafter referred to as “element size”) of the film surface of the multilayer film is decreased, the change in resistance (ΔR) and the reproduction output cannot be effectively increased, and that the magnetic sensor described above cannot be used in practice.
The current photolithographic technique has a limitation of decreasing the area of the film surface of the multilayer film. In addition, when the total thickness is increased, the gap length is increased, and as a result, there has been a problem in that the reproduction properties may be degraded in some cases.
Hence, in order to improve the change in resistance (ΔR), methods have been disclosed in several documents in which a current path flowing through the multilayer film is squeezed by a member provided in addition to the multilayer film.
FIG. 15 is a copy of the structure of a magnetic sensor in a manufacturing step shown in FIG. 7 of U.S. Pat. No. 6,353,318 B1 and is a partial cross-sectional view of the magnetic sensor when it is viewed from a face facing a recording medium.
Reference numeral 1 indicates a lower electrode layer, and on the lower electrode layer 1, a multilayer film 2 exhibiting a magnetoresistance effect is formed. On the multilayer film 2, a resist layer 3 is provided, and two end surfaces 2a of the multilayer film 2 in a track width direction (X direction in the figure) which are not overlapped with the resist layer 3 are milled to form inclined surfaces.
As shown in FIG. 15, on the two end surfaces 2a of the multilayer film 2, lower insulating layers (lower insulator) 4 are formed. The lower insulators 4 are also formed inside cutaway parts 3a formed in both sides of a lower portion 3c of the resist layer 3 in the track width direction and are arranged on an upper surface 2b of the multilayer film 2 with a predetermined gap 4a therebetween in the track width direction (X direction in the figure).
A layer indicated by reference numeral 5 on the lower insulator 4 is an underlayer, reference numeral 6 indicates a permanent magnetic layer, and an inside front portion of an upper insulating layer (upper insulator) 7 formed on the permanent magnetic layer 6 extends inside the cutaway part 3a of the resist layer 3 so as to overlap the lower insulator 4.
As for the magnetic sensor shown in FIG. 15, first, on the entire surface of the lower electrode layer 1, the multilayer film 2 is formed; the resist layer 3 is then formed on an optional position of the multilayer film 2; the two end surfaces 2a of the multilayer film 2 which are not overlapped with the resist layer 3 are milled; and on each of the two end surfaces 2a, the lower insulator 4, the underlayer 5, the permanent magnetic layer 6, and the upper insulator 7 are sequentially formed. Next, the resist layer 3 is removed, and over the upper insulators 7 to the multilayer film 2 exposed through the gap 4a provided between the lower insulators 4, an upper electrode layer (not shown in the figure) is formed.
In the method for manufacturing a magnetic sensor described in U.S. Pat. No. 6,353,318 B1, as shown in FIG. 15, the lower insulators 4 can be disposed on the upper surface 2b of the multilayer film 2 with the predetermined gap 4a therebetween in the track width direction.
Accordingly, it has been believed that a path of current flowing through the multilayer film 2 is the width region of the gap 4a provided between the lower insulators 4 on the upper surface 2a of the multilayer film 2, and that squeezing of the current can be appropriately performed.
However, According to U.S. Pat. No. 6,353,318 B1, the formation of the lower insulators 4 is performed after the end surfaces 2a of the multilayer film 2 are milled. Accordingly, since a magnetic powder is generated when the multilayer film 2 is milled and then adheres to the peripheries of an upper portion 3b and a lower portion 3c of the resist layer 3, due to this adhesion of the magnetic powder, the space in the cutaway part 3a is decreased. Alternatively, when the lower insulators 4 are formed, the magnetic powder described above adheres to the periphery of the upper portion 3b of the resist layer 3, and as a result, the shadow effect is enhanced. Consequently, it becomes difficult to appropriately form the lower insulators 4 inside the cutaway parts 3a. 
The lower insulator 4 is formed, for example, by sputtering at an angle inclined with respect to the direction perpendicular to the surface of a substrate (not shown in the figure); however, since the space inside the cutaway part 3a is decreased, and/or the shadow effect is enhanced, even when the film formation is performed by sputtering along an inclined direction, the length of the lower insulator 4 provided on the upper surface 2b of the multilayer film 2 is decreased. That is, the gap 4a provided between the lower insulators 4 is increased, and as a result, a current-squeezing structure cannot be effectively realized. In addition, the thickness of the lower insulator 4 provided on the upper surface 2a of the multilayer film 2 is liable to be decreased as compared to a predetermined dimension. According to the related technique shown in FIG. 15, since the upper insulator 7 is further provided on the lower insulator 4 which is formed on the upper surface 2a of the multilayer film 2, it may be believed that the insulation between the multilayer film 2 and the upper electrode layer except for the gap 4a provided between the lower insulators 4 can be ensured by the two layers described above. However, in practice, at the stage prior to the formation of the upper insulator 7, since the same material layers as the lower insulator 4, the underlayer 5, and the permanent magnetic layer 6 adhere to the periphery of the resist layer 3, the space in the cutaway part 3a of the resist layer 3 is further decreased, and the shadow effect is also further enhanced. Hence, the formation of the upper insulator 7 extending inside the cutaway part 3a is more difficult than the formation of the lower insulator 4 extending along the upper surface 2b of the multilayer film 2, and it is believed that except for the gap 4a provided between the lower insulators 4, the insulation between the multilayer film 2 and the upper electrode layer is significantly decreased. In view of the points described above, the method for manufacturing a magnetic sensor, shown in FIG. 15, cannot effectively form the current path-squeezing structure.
Next, FIG. 16 is a copy of the structure of a magnetic sensor in a manufacturing step shown in FIG. 10 of U.S. Pat. No. 6,421,212 B1 and is a partial cross-sectional view of the magnetic sensor when it is viewed from a face facing a recording medium. FIG. 16 shows only around the right side region of the magnetic sensor in a manufacturing step. FIG. 17 is a partial cross-sectional view of a magnetic sensor in a manufacturing step when it is viewed from a face facing a recording medium. The magnetic sensor mentioned above is not shown in U.S. Pat. No. 6,421,212 B1; however, in consideration of the description thereof, it is believed that the magnetic sensor in a manufacturing step following the step shown in FIG. 16 is in the state as shown in FIG. 17. As FIG. 16, FIG. 17 also shows only around the right side region of the magnetic sensor in a manufacturing step.
Reference numeral 10 indicates a substrate, a lower electrode layer 11 is formed on the substrate 10, a multilayer film 12 exhibiting a magnetoresistance effect is formed on the lower electrode layer 11, and a protective layer 13 is formed on the multilayer film 12. The protective layer 13 is formed of an inorganic insulating material such as Al2O3 or SiO2.
As shown in FIG. 16, on the protective layer 13, a resist layer 17 is formed. As shown in FIG. 16, the two end surfaces 14 of the lower electrode layer 11, the multilayer film 12, and the protective layer 13 are milled, insulating layers 15 are formed over the two end surfaces 14 to the substrate 10. In addition, on the insulating layers 15, bias layers 16 are formed.
For forming the magnetic sensor in the state shown in FIG. 16, after the lower electrode layer 11, the multilayer film 12, and the protective layer 13 are first formed on the substrate 10, the resist layer 17 is formed by exposure and development on the protective layer 13 so as to have a predetermined shape, and the two end surfaces 14 of the lower electrode layer 11, the multilayer 12, and the protective layer 13, which are not overlapped with the resist layer 17 are milled. Subsequently, the insulating layers 15 are formed over the two end surfaces 14 to the substrate 10, and on the insulating layers 15, the bias layers 16 are formed.
In the step shown in FIG. 17, in order to form an opening portion (gap) for supplying current into the multilayer film 12 from an upper electrode layer (not shown in the figure), for example, a resist layer 18 is formed on the protective layer 13, and an opening portion 18a is formed in the resist layer 18 located on the center of the protective layer 13 by exposure and development. Next, the protective layer 13 exposed through this opening portion 18a is removed by etching or the like as shown by a dotted line to form a opening portion 13a in the protective layer 13, and the upper surface of the multilayer film 12 is exposed through this opening portion 13a. The region of the upper surface of the multilayer film 12 thus exposed is to be used as a current path.
According to the magnetic sensor described in U.S. Pat. No. 6,421,212 B1, the protective layer 13 is formed on the multilayer film 12 beforehand, and the opening portion 13a is formed in the protective layer 13 in a subsequent step so that the current pass-squeezing structure is realized for the multilayer film 12.
However, according to the method for manufacturing a magnetic sensor, shown in FIGS. 16 and 17, when the opening portion 13a is provided in the protective layer 13, etching therefor has influence on the multilayer film 12 present under the protective layer 13, and as a result, the upper surface of the multilayer film 12 may be damaged with a high probability.
In addition, since the resist layer 17 in the step shown in FIG. 16 is removed, and subsequently, the resist layer 18 is again formed, the alignment accuracy for forming the opening portion 18a in the resist layer 18 is decreased, and as a result, a problem may arise in that the opening portion 13a cannot be formed at a predetermined position of the protective layer 13. In addition, due to the limitation of photolithographic techniques, it is extremely difficult to form a minute opening portion 18a in the resist layer 18 with high accuracy.